it says that it might not work all the right way cause its open box should I be worried?

What it says is that open box products may or may not come with accessories, even if they are crucial to the product working. Right?

The only accessories that can be missing are the manual (available online), the driver cd (again, download the drivers from asus' site), the backplate (makes no real difference), and sata cblaes ($2 each)

most will come with everything, but even if they come with only the board, it is an epic deal.